This invention relates to initializing apparatus for a dynamic memory and more particularly to apparatus which, in conjunction with circuit means for periodically refreshing the data represented by a voltage stored in the cells thereof, causes voltage representing binary data, zeros or ones, to be written into the memory cells of such a memory during each refresh cycle after power is initially applied to the memory until all the cells of each array of the memory have been initialized, i.e., data has been written into them.
In modern data processing equipment many advantages are achieved by utilizing insulated gate field effect transistors known as MOS transistors or MOSFET transistors for the memory cells of a digital computer. Either P-channel or N-channel device may be utilized for this purpose. Memory cells utilizing MOS transistors require less complex processing techniques and permit a greater packing density which characteristics result in considerable savings in the cost of such memories and in the volume occupied by them. This is particularly important because of the large number of memory cells required by modern computers.
Dynamic memories utilizing MOS transistors have some disadvantages which have limited their use in modern data processing equipment. One of the disadvantages of a dynamic MOS memory is that data represented by a voltage stored in a cell deteriorates or decreases in value relatively rapidly as a function of time and thus must be periodically refreshed or restored if the validity or accuracy of the data is to be maintained. Thus, such a memory must necessarily include circuitry which periodically provides refresh cycles so that the voltage stored in each cell is restored substantially to its original value periodically before the probability of the data being valid or correct is reduced to an unacceptably low value.
Another disadvantage of dynamic memories utilizing MOS transistors for the storage of data occurs when power is initially applied to the memory. At that time the voltages stored in the cells in at least enough of the cells to be statistically significant will have values representing binary data such that any error detection and correction means (EDAC), such as are generally associated with such a memory, will sense uncorrectable errors. In some memory systems with EDAC the presence of such errors prevents or inhibits data from being written into some of the cells at a memory location or address if such an error or errors are detected in data stored at that address.
In prior dynamic MOS memories the problems associated with the initial application of power to the memory was solved by loading or reading into all the locations of the memory data from an appropriate source, sometimes known as bootloading the memory. In bootloading a memory, magnetic tapes or punch cards, for example, provide the data to be written into the cells of the memory. A disadvantage of bootloading a memory is that bootloading requires a considerable period of time and also requires that all of the subsystems of a computer system be utilized to accomplish it.
The disadvantages of the prior art are alleviated by the present invention by supplementing the circuits required to periodically refresh the memory cells of the dynamic memory so that when power is initially applied to the memory the refresh circuitry is supplemented so that it has the capability of writing data into each of the memory cells of each of the arrays constituting such memory. The rate at which this happens is one cell per array per refresh cycle. This function continues until all the cells of each array of the memory have data written into them in this manner. Thus, the present invention eliminates the need for bootloading data from punch cards, magnetic tape, or magnetic disks when a computer memory is initially energized.
It is therefore an object of this invention to provide new and improved apparatus for initializing a dynamic memory.
Another object of this invention is to provide simplified apparatus for initializing a dynamic memory.
A further object of this invention is to provide apparatus for initializing a dynamic memory without using data from peripherals such as punch cards, magnetic tapes, and magnetic disks.
Still another object of this invention is to provide apparatus which initializes the dynamic memory storage cells of such a memory by supplementing the refresh cycle circuits of the dynamic memory so that such circuits can be used to write data into the cells of the memory.